Caption: Quadriceps muscle surgery. View of a surgical incision of the knee of a male patient, showing a ruptured quadriceps muscle. The thigh is at far left; the knee appears white at right. Quadriceps muscle (centre left) has torn from its attachment producing a gap at centre. The quadriceps is a powerful muscle divided into four parts, located at the front of the thigh. It straightens the knee and lower leg. Its upper ends attach to the pelvis and upper thigh-bone, while the lower ends seen here merge with a tendon attached to the tibia shin-bone. Sudden stretching of the leg may tear this muscle which may then require surgery.